Re: [6.2 regression][bisected]discard storm on idle since v6.1-rc8-59-g63a7cb130718 discard=async

Michael Bromilow
2023-04-10T02:03:44Z

On 04/04/2023 19:51, Boris Burkov wrote:
> On Tue, Apr 04, 2023 at 02:15:38PM -0400, Chris Mason wrote:
>> So, honestly from my POV the async discard is best suited to consumer
>> devices. Our defaults are probably wrong because no matter what you
>> choose there's a drive out there that makes it look bad. Also, laptops
>> probably don't want the slow dribble.
>
> Our reasonable options, as I see them:
> - back to nodiscard, rely on periodic trims from the OS.
> - leave low iops_limit, drives stay busy unexpectedly long, conclude that
> that's OK, and communicate the tuning/measurement options better.
> - set a high iops_limit (e.g. 1000) drives will get back to idle faster.
> - change an unset iops_limit to mean truly unlimited async discard, set
> that as the default, and anyone who cares to meter it can set an
> iops_limit.
>
> The regression here is in drive idle time due to modest discard getting
> metered out over minutes rather than dealt with relatively quickly. So
> I would favor the unlimited async discard mode and will send a patch to
> that effect which we can discuss.

Will power usage be taken into consideration? I only noticed this regression
myself when my laptop started to draw a constant extra ~10W from the constant
drive activity, so I imagine other laptop users would also prefer a default
which avoids this if possible. If "relatively quickly" means anything more
than a few seconds I could see that causing rather significant battery life
reductions.

- Michael